In that regard, the insertion of the weft thread is monitored by at least one sensor. After each starting process, during at least the first weaving cycle, the weaving machine is operated in slow speed running.
The at least first inserted weft thread is held against springing back into the loom shed at the outlet side of the loom shed at least until the interlacing or binding thereof by warp threads.
Several weft thread detecting and stretching apparatuses are already known, for example from the DE 198 02 254 C1 and the DE 198 10 129 B4. However, these documents do not pertain to the behavior of weft yarns during the weft insertion in various different rotational speed ranges of the weaving machine, for example at a new start of the weaving machine.
In the production of selected woven webs or fabrics, such as for example jeans fabrics and fabrics with a twill weave or binding on air-jet weaving machines, it has been found to be advantageous, especially with respect to achieving a woven ware without start-up marks, after each start of the weaving machine, the first weaving cycle, namely with reference to the rotational angle of the main drive shaft, to operate or drive the first full rotation of the main drive shaft in the slow speed running, namely with less than 200 min−1. The above described technology in the operation of air-jet weaving machines is known for a long time under the term “single weft or shot automatic”. In an air-jet weaving machine, the process of the weft thread insertion itself is not concerned or affected by the slow speed running; the weft thread insertion occurs in consideration of the time duration necessary therefor in such a manner as if the air-jet weaving machine would already operate with a predetermined operating rotational speed directly after the starting process.
The weft thread that is thus inserted in a time of a few milliseconds across the weaving width into the loom shed is to be held by suitable means at the outlet side of the loom shed, thus on the side of the loom shed lying opposite the weft thread insertion, for so long until it is beat-up against the woven web edge by the weaving reed and is interlaced or bound by the shed-forming warp threads. In air-jet weaving machines, the inserted weft thread is held on the outlet extraction side of the loom shed in a known manner by pneumatically acting stretching or sucking nozzles. In the processing of weft yarns with relatively low ripping or tearing strength it can be determined, that during the weaving cycle directly following the start of the weaving machine, in which the weaving machine is operated in the slow speed running, the applicable weft thread is impaired under the effect of the holding means in such a manner that a weft thread break arises before the binding of the weft thread by the warp threads. In such a case, the part of the weft thread remaining on the insertion side “springs” back into the loom shed that is not yet completely closed, and thereby produces a defect in the woven web or fabric.